U.S. patent number 4,902,551 [Application Number 07/224,911] was granted by the patent office on 1990-02-20 for process for treating copper surface.
This patent grant is currently assigned to Hitachi Chemical Company, Ltd.. Invention is credited to Yuko Kimura, Akishi Nakaso, Haruo Ogino, Toshiro Okamura, Tomoko Watanabe.
United States Patent |
4,902,551 |
Nakaso , et al. |
February 20, 1990 |
Process for treating copper surface
Abstract
Adhesion of copper to a resin layer is improved by reducing a
copper oxide layer with an aqueous aldehyde solution (a) while
applying a potential of -1000 mV to -400 mV to the copper oxide
layer, (b) after contacting with a metal piece made of copper or a
metal nobler than copper, or (c) after contacting with an aqueous
solution of alkali borohydride.
Inventors: |
Nakaso; Akishi (Oyama,
JP), Okamura; Toshiro (Shimodate, JP),
Ogino; Haruo (Shimodate, JP), Watanabe; Tomoko
(Ibaraki, JP), Kimura; Yuko (Shimodate,
JP) |
Assignee: |
Hitachi Chemical Company, Ltd.
(Tokyo, JP)
|
Family
ID: |
18069094 |
Appl.
No.: |
07/224,911 |
Filed: |
July 27, 1988 |
Foreign Application Priority Data
|
|
|
|
|
Dec 14, 1987 [JP] |
|
|
62-315750 |
|
Current U.S.
Class: |
428/137; 148/269;
156/151; 156/253; 156/314; 428/901; 29/852; 148/272; 156/281;
205/152; 216/35 |
Current CPC
Class: |
B32B
27/281 (20130101); B32B 15/20 (20130101); B32B
27/38 (20130101); B32B 15/098 (20130101); B32B
15/12 (20130101); H05K 3/022 (20130101); B32B
27/42 (20130101); B32B 15/14 (20130101); C23C
22/83 (20130101); H05K 3/385 (20130101); B32B
15/04 (20130101); B32B 15/092 (20130101); B32B
15/08 (20130101); H05K 3/4652 (20130101); C23C
18/40 (20130101); C23C 22/63 (20130101); B32B
2457/08 (20130101); H05K 2203/0315 (20130101); H05K
3/281 (20130101); Y10S 428/901 (20130101); H05K
1/0393 (20130101); Y10T 156/1057 (20150115); Y10T
29/49165 (20150115); H05K 3/427 (20130101); Y10T
428/24322 (20150115); B32B 2311/12 (20130101); H05K
2201/0355 (20130101); H05K 2203/1157 (20130101); H05K
1/0366 (20130101) |
Current International
Class: |
B32B
15/04 (20060101); C23C 22/63 (20060101); C23C
22/83 (20060101); C23C 18/31 (20060101); C23C
18/40 (20060101); C23C 22/05 (20060101); C23C
22/82 (20060101); H05K 3/38 (20060101); H05K
3/02 (20060101); H05K 3/46 (20060101); H05K
3/28 (20060101); H05K 3/42 (20060101); H05K
1/03 (20060101); H05K 1/00 (20060101); B32B
003/10 (); B44C 001/22 () |
Field of
Search: |
;156/151,314,253,630,281,902 ;148/6.14R,269,272 ;204/27,38.1
;428/137,901 ;29/852 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Gallagher; John J.
Attorney, Agent or Firm: Antonelli, Terry & Wands
Claims
What is claimed is:
1. A process for treating a copper surface which comprises
forming a copper oxide layer on a copper surface by treating with
an aqueous solution containing an oxidizing agent, and
treating the copper oxide layer with an aqueous aldehyde solution
having a pH of 9.0 or higher to reduce the copper oxide,
said treatment of the copper oxide layer being carried out
(a) while applying a potential of -1000 mV to -400 mV in terms of
Ag-AgCl electrode to the copper oxide layer, or
(b) after contacting the copper oxide layer with a contacting piece
made of copper or a metal nobler than copper, or
(c) after contacting the copper oxide layer with an aqueous
solution containing an alkali borohydride so as to make the
potential of copper in the range of -1000 mV to -400 mV in terms of
Ag-AgCl electrode.
2. A process according to claim 1, wherein the treatment of the
copper oxide layer is carried out while applying a potential of
-1000 mV to -400 mV in terms of Ag-AgCl electrode to the copper
oxide layer.
3. A process according to claim 2, wherein the potential is applied
by contacting with copper or a metal nobler than copper.
4. A process according to claim 1, wherein the treatment of the
copper oxide layer is carried out after contacting the copper oxide
layer with a contacting piece made of copper or a metal nobler than
copper.
5. A process according to claim 4, wherein the contacting piece is
made in the form of roll covered with a copper layer or a layer of
a metal nobler than copper.
6. A process according to claim 1, wherein the treatment of the
copper oxide layer is carried out after contacting the copper oxide
layer with an aqueous solution containing an alkali borohydride so
as to make the potential of copper in the range of -1000 mV to -400
mV in terms of Ag-AgCl electrode.
7. A process according to claim 6, wherein the alkali borohydride
is sodium borohydride.
8. A copper-clad laminate obtained by
subjecting one or both surfaces of copper foil to the surface
treatment process of claim 1,
laminating one or more of the surface treated copper foils and one
or more sheets of glass cloth or paper impregnated with an epoxy
resin, a phenol resin or a polyimide resin or one or more sheets of
an epoxy resin, a phenol resin or a polyimide resin mixed with
glass fibers, or laminating one or more of the thus surface treated
copper foils coated with an epoxy resin, and
subjecting the resulting multiple layers to heating and pressing
treatment to form a laminated unit having copper layers on the
outermost surfaces.
9. A copper-clad flexible film obtained by
subjecting one or both surfaces of copper foil to the surface
treatment process of claim 1, and
bonding a flexible resin film to the resulting copper foil using an
adhesive of epoxy resin or acrylic resin so as to have copper
layers on the outermost surfaces.
10. A copper-clad flexible film according to claim 9, wherein the
flexible resin film is made from polyimide, polyester,
polytetrafluoroethylene, polysulfone, or polyether ether
ketone.
11. A multi-layer wiring board obtained by
laminating one or more copper foils and one or more sheets of glass
cloth or paper impregnated with an epoxy resin, a phenol resin or a
polyimide resin or one or more sheets of an epoxy resin, a phenol
resin or a polyimide resin mixed with glass fibers, or laminating
one or more copper foils coated with an epoxy resin, a phenol resin
or a polyimide resin,
subjecting the resulting multiple layers to heating and pressing
treatment to form a copper-clad laminate,
removing unnecessary portions from the copper foil of the laminate
by etching to form a circuit pattern for an internal layer,
subjecting the copper foil thus treated to the surface treatment
process of claim 1,
laminating on the resulting copper surface an epoxy resin, a phenol
resin or a polyimide resin, or a glass cloth or paper impregnated
with an epoxy resin, a phenol resin or a polyimide resin, or
laminating a sheet of an epoxy resin, a phenol resin or a polyimide
resin mixed with glass fibers, with repetition of laminating to
form multiple layers and a copper foil as an outermost layer,
subjecting the multiple layers and copper foil to heating and
pressing treatment to form a laminated unit having copper layers on
the outermost surfaces,
drilling through-holes in the laminated unit,
metallizing inner walls of the through-holes, and
removing unnecessary portions from the outermost copper layers by
etching to form circuits.
12. A multi-layer wiring board obtained by
laminating one or more copper foils and one or more sheets of glass
cloth or paper impregnated with an epoxy resin, a phenol resin or a
polyimide resin or one or more sheets of an epoxy resin, a phenol
resin or a polyimide resin mixed with glass fibers, or laminating
one or more copper foils coated with an epoxy resin, a phenol resin
or a polyimide resin,
subjecting the resulting multiple layers to heating and pressing
treatment to form a copper-clad laminate,
removing unnecessary portions from the copper foil of the laminate
by etching to form a circuit pattern for an inner layer,
subjecting the copper foil thus treated to the surface treatment
process of claim 1,
laminating on the resulting copper surface an epoxy resin, a phenol
resin or a polyimide resin, or a glass cloth or paper impregnated
with an epoxy resin, a phenol resin or a polyimide resin, or
laminating a sheet of an epoxy resin, a phenol resin or a polyimide
resin mixed with glass fibers, with repetition of laminating to
form multiple layers and a copper foil subjected to the surface
treatment process of claim 1 as an outermost layer,
subjecting the multiple layers and copper foil to heating and
pressing treatment to form a laminated unit having copper layers on
the outermost surfaces,
drilling through-holes in the laminated unit,
metallizing inner walls of the through-holes, and
removing unnecessary portions from the outermost copper layers by
etching to form circuits.
13. A flexible wiring board obtained by
bonding a copper foil to a flexible resin film using an adhesive of
epoxy resin or acrylic resin to form a copper-clad flexible
film,
removing unnecessary portions from the copper foil by etching to
form a circuit pattern for an inner layer,
subjecting the copper foil thus treated to the surface treatment
process of claim 1, and
bonding a flexible resin film from which necessary portions for
connection are removed to the thus treated copper surface with an
adhesive of epoxy resin or acrylic resin.
14. A flexible wiring board according to claim 13, wherein the
flexible resin film is made from polyimide, polyester,
polytetrafluoroethylene, polysulfone, or polyether ether ketone.
Description
BACKGROUND OF THE INVENTION
This invention relates to a process for treating a copper surface
suitable for making copper on an internal layer circuit board
adhere to a prepreg in a step for laminating internal layer circuit
boards and prepregs alternately for producing a multi-layer printed
wiring board.
Multi-layer printed circuit boards have been produced by removing
unnecessary portions of copper foils of upper-clad laminates by,
for example, etching to form internal layer circuits, roughening
the copper surfaces of internal layer circuits with a chemical
fluid, subjecting the roughened surfaces to oxidation treatment,
piling prepregs and copper foils which become outer layer circuits
on a plurality of internal layer circuit boards and laminating them
into one body, drilling holes at portions necessary for connecting
the outer layer circuits and the internal layer circuits, removing
resins and pieces of glass sticked to surfaces of the holes with a
chemical treating fluid, forming a metal layer such as a copper
layer by electroless plating or the like, and forming outer layer
circuits by etching or the like. In such a process, the oxidation
treated layer of copper surface exposed on the surfaces of holes is
easily corroded by the acidic chemical treating fluid in a later
step to form portions wherein no adhesion is maintained between the
internal layer copper foils and prepregs around the holes
(so-called pink rings), which results in bringing about peeling by
a thermal shock such as soldering.
In order to form a surface hardly dissolved with the chemical
treating fluid which is more acidic than copper oxide, Japanese
Patent Unexamined Publication No. 56-153797 discloses a process
wherein the copper oxide formed is reduced by dipping in an alkali
solution such as a solution of sodium borohydride, formaldehyde or
the like. But when copper oxide is reduced by using a sodium
borohydride solution, the surface appearance is blurred after the
treatment and adhesion of prepregs often becomes insufficient. On
the other hand, when an aqueous solution of formaldehyde is used,
there takes place a problem that the treating rate is small.
On the other hand, in order to improve adhesion between a metal and
a resin in the production of multi-layer printed wiring boards,
there are proposed the use of an amineboran as a reducing agent for
copper oxide (Japanese Patent Unexamined Publication No.
61-176192), the treatment of copper oxide with an activating
solution including a catalytic metal element before the reduction
to copper (Japanese Patent Unexamined Publication No. 61-279531),
the use of a reducing agent solution dispersing metal particles
having a catalytic ability therein (Japanese Patent Unexamined
Publication No. 61-266228), and the exposure of metallic copper on
a part of a copper surface covered with a copper oxide layer when
the copper oxide layer is reduced with a reducing agent solution
(Japanese Patent Unexamined Publication No. 61-250036). But the
adhesive strength between the metal (copper) and the resin is still
insufficient for practical use according to these proposals.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a process for treating
a copper surface, particularly in the production of multi-layer
printed wiring boards, overcoming disadvantages of the prior art
techniques and giving strong adhesive strength between a copper
layer and a resin layer with a fast treating speed.
This invention provides a process for treating a copper surface
which comprises
forming a copper oxide layer on a copper surface by treating with
an aqueous solution containing an oxidizing agent, and
treating the copper oxide layer with an aqueous aldehyde solution
having a pH of 9.0 or higher to reduce the copper oxide,
said treatment of the copper oxide layer being carried out
(a) while applying a potential of -1000 mV to -400 mV in terms of
Ag-AgCl electrode to the copper oxide layer,
(b) after contacting the copper oxide layer with a contacting piece
made of copper or a metal nobler than copper, or
(c) after contacting the copper oxide layer with an aqueous
solution containing an alkali borohydride so as to make the
potential of copper surface in the range of -1000 mV to -400 mV in
terms of Ag-AgCl electrode.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A copper oxide layer in fine relief is first formed on a copper
surface by treating with an aqueous solution containing an
oxidizing agent.
As the oxidizing agent, there can be used sodium chlorite,
potassium persulfate, potassium chlorate, potassium perchlorate,
etc.
The treatment can be carried out by dipping,spraying, or the
like.
A typical example of the copper oxide treating aqueous solution is
as follows:
______________________________________ NaClO.sub.2 5-150 g/l
NaPO.sub.4.12H.sub.2 O 10-60 g/l NaOH 1-50 g/l
______________________________________
Preferable treating conditions are to use the treating aqueous
solution at temperature of 55.degree. to 95.degree. C. with a
contact time of 15 seconds or more.
The treating aqueous solution may further contain one or more
OH.sup.- ion sources and/or one or more buffering agents such as
trisodium phosphate, etc.
It is preferable to conduct a pretreatment of the copper surface
before forming a copper oxide layer by contacting the copper
surface with an aqueous solution of ammonium persulfate or cupric
chloride and hydrochloric acid for roughening the copper surface
after degreasing.
After the formation of the copper oxide layer, reduction of the
copper oxide layer is carried out by treating with an aqueous
aldehyde solution having a pH of 9.0 or higher combined with one of
the following three treatments:
(a) while applying a potential of -1000 mV to -400 mV in terms of
Ag-AgCl electrode (i.e. when measured by using an Ag-AgCl
electrode) to the copper oxide layer,
(b) after contacting the copper oxide layer with a contacting piece
made of copper or a metal nobler than copper, and
(c) after contacting the copper oxide layer with an aqueous
solution containing an alkali borohydride so as to make the
potential of copper surface in the range of -1000 mV to -400 mV in
terms of Ag-AgCl electrode.
According to the method (a), the reduction of copper oxide layer is
carried out as follows.
The copper oxide layer in fine relief is reduced to metallic copper
by treating with an aqueous aldehyde solution, while applying a
potential of -1000 mV to -400 mV in terms of Ag-AgCl electrode to
the copper oxide layer, at least for a while. As the aldehyde,
there can be used formaldehyde, paraformaldehyde, an aromatic
aldehyde such as benzaldehyde. The pH of the aldehyde aqueous
solution is 9.0 or higher, preferably 10.5 or higher. The higher
the pH becomes, the stronger the reducing power becomes. As a pH
adjusting agent, there can be used an alkali hydroxide such as
NaOH.
The adding amount of the aqueous aldehyde solution is preferably
0.01 mole/l or more, more preferably 0.02 mole/l or more. Too high
concentration is not preferable due to worsening of working
circumstances.
The temperature of the aqueous aldehyde solution is not limited so
long as maintaining the aqueous solution. Generally speaking, since
the activity is lowered with lowering of the solution temperature,
it is necessary to enhance the concentration of the aldehyde
solution.
The potential of the copper oxide layer in the aqueous aldehyde
solution is about -150.+-.100 mV in terms of Ag-AgCl electrode. But
such a high voltage is not preferable to start the reducing
reaction rapidly. In contrast, by applying a potential of -1000 mV
to -400 mV in terms of Ag-AgCl electrode to the copper oxide layer
at least for a while, for example, even 1 second or less, the
reducing reaction can be started remarkably fast. The potential of
-1000 mV to -500 mV is more preferable. In order to maintain the
potential at such a low value, the copper oxide layer may be
contacted with copper or a noble metal such as platinum, palladium,
or the like in the aqueous aldehyde solution. The potential of -400
mV or lower can also be obtained by using a constant potential
source. In this case, the object is to supply the potential, and
thus a small current may be applicable.
The time necessary for treating with the aqueous aldehyde solution
is that necessary for making the potential of treating surface -400
mV, or lower preferably -500 mV or lower, in the aqueous aldehyde
solution in terms of Ag-AgCl electrode, except for the operation
for maintaining at the lower potential state. Usually, the period
of 120 seconds or more is necessary.
The metallic copper has a potential of about -800.+-.200 mV in
terms of Ag-AgCl electrode in the aqueous aldehyde solution.
Therefore, when the potential is lower than -500 mV, at least a
part of copper oxide can be reduced.
According to the method (b), the reduction of copper oxide layer is
carried out as follows.
After contacting the copper oxide layer with a contacting piece
made of copper or a metal nobler than copper, the copper oxide
layer is reduced to metallic copper by treating with an aqueous
aldehyde solution having a pH of 9.0 or higher.
As to the contacting piece, it is sufficient that the surface
portion of contacting piece is made of copper or a metal nobler
than copper. Examples of the metal nobler than copper are gold,
platinum, palladium, and the like. The contacting piece can
preferably take a form of a roll. One example of such a roll is a
rubber roll, the surface of which is covered with a cloth plated
with a metal as mentioned above. A copper plated cloth manufactured
by Seren K.K. is available commercially. It is more preferable to
use a cloth plated with a noble metal such as gold, palladium, or
the like in addition to copper plating.
It is also possible to use a rod capable of conducting surface
contact to some extent, a brush, or a cloth, in place of the
roll.
It is sufficient that the contacting piece relatively move on the
copper oxide layer. That is, either one of the contacting piece or
the copper oxide layer can be moved, or both of them can be moved.
For example, a substrate having the copper oxide layer thereon is
moved by one or more rolls. It is preferable to slide the
contacting piece and the copper oxide layer while keeping point or
surface contact such as contacting a freely movable roll with the
moving substrate. In order to speed up the contacting process, it
is preferable to use a plurality of pairs of rolls facing each
other in series. In the case of using a cloth as the contacting
piece, it is possible to move the cloth and the copper oxide layer
while surface contacting them to some extent and sliding. It is
also possible to reduce copper oxide by treating with the aqueous
aldehyde solution having a pH of 9 or higher, while relatively
moving the copper oxide layer and the contacting piece and keeping
point or surface contacting of the two. The treatment with the
aqueous aldehyde solution can be carried out by dipping, spraying
and the like.
As the aldehyde, there can be used formaldehyde, paraformaldehyde,
an aromatic aldehyde such as benzaldelhyde. The pH of the aldehyde
aqueous solution is 9.0 or higher, preferably 10.5 or higher. The
higher the pH becomes, the stronger the reducing power becomes. As
a pH adjusting agent, there can be used an alkali hydroxide such as
NaOH.
The adding amount of the aldehyde aqueous solution is preferably
0.01 mole/l or more, more preferably 0.02 mole/l or more. Too high
concentration is not preferable due to worsening of working
circumstances.
The copper oxide formed on the copper surface has fine concaves and
convexes with several microns. By the effect of such shapes, the
adhesive strength to a prepreg resin layer to be laminated can be
improved.
Further, since the aqueous aldehyde solution having a pH of 9.0 or
higher has a reducing power, copper oxide is reduced in contact
with the aqueous aldehyde solution. Further, since fine relief
shape can be retained after the reduction, the adhesive strength to
the resin layer to be laminated can be improved, and the adhesion
interface is made resistant to an acidic solution and an
electroless copper plating bath.
By contacting the copper oxide layer with the contacting piece, the
reduction of copper oxide takes place rapidly when contacted with
the aqueous aldehyde solution having a pH of 9.0 or higher. Thus,
the time necessary for reducing copper oxide is shortened
remarkably and can be within several minutes for completing the
reduction.
When one or more rolls are used as the contacting piece, the
reducing treatment of copper oxide can be carried out continuously.
Recently, wiring of copper conductor on a printed wiring board has
independent portions and miniaturized, but uniform contact becomes
possible by using a roll as the contacting piece.
According to the method (c) the reduction of copper oxide layer is
carried out as follows.
After contacting the copper oxide layer with an aqueous solution
containing an alkali borohydride so as to make the potential of
copper surface in the range of -1000 mV to -400 mV in terms of
Ag-AgCl electrode, the copper oxide layer is reduced to metallic
copper by treating with an aqueous aldehyde solution having a pH of
9.0 or higher.
As the alkali borohydride which is used as a reducing agent, there
can be used sodium borohydride, potassium borohydride, etc. The
concentration of alkali borohydride influences a changing rate of
the potential of copper surface subjected to oxidation treatment
and uniformity of surface appearance after the reduction. The
concentration of alkali borohydride is preferably 0.1 g/l or more,
more preferably 0.2 to 5 g/l. Since the alkali borohydride is
easily decomposed naturally, it is preferable to add lead acetate,
lead chloride, lead sulfate, or thioglycolic acid in order to
prevent the decomposition. The decomposition can also be prevented
by making the pH 10 to 13.
The contact time between the copper surface subjected to oxidation
treatment and the alkali borohydride is extremely important. When
the oxidation treated copper surface is contacted with the alkali
borohydride, copper oxide begins its reduction. The potential of
oxidation treated copper surface changes to a lower side. In this
case, when the contact time is prolonged until the potential
becomes lower than -1000 mV, non-uniformity of surface appearance
often takes place to stop the improvement of adhesive strength. In
order to prevent such a problem, the potential of -1000 mV to -400
mV should be maintained. In practice, it is not necessary to watch
the potential always. Preferable contact time can be determined by
the composition and temperature of the aqueous alkali borohydride
solution. For example, in the case of sodium borohydride with a
concentration of 1 g/l, pH 12.5, and a temperature of 40.degree.
C., a preferable contact time is 3 to 180 seconds.
As the aqueous aldehyde solution, the same one as used in the
method (b) mentioned above can also be used.
When the copper surface subjected to the treatment with the aqueous
alkali borohydride solution is contacted with the aqueous aldehyde
solution, the initial potential of copper is in the range of -1000
mV to -400 mV in terms of Ag-AgCl electrode. When the contact is
continued, the potential is changed to be lower than -1000 mV which
is the potential of metallic copper. The time necessary for
contacting with the aqueous aldehyde solution is one until the
potential of copper becomes not lower than -1000 mV. In practice,
the contact time is changed depending on the composition,
concentration, and temperature of the aqueous aldehyde solution.
For example, when a 36% formaldehyde aqueous solution with a
concentration of 4 ml/l, pH 2.5 and a temperature of 50.degree. C.
is used, preferable contact time is 180 seconds.
The copper surface subjected to the aqueous alkali borohydride
solution treatment can directly be contacted with the aqueous
aldehyde solution, or washed with water, followed by contact with
the aqueous aldehyde solution.
The copper surface treatment of this invention can be applied to
not only the pretreatment of internal circuits to be subjected to
multi-layer adhesion, but also circuit surface treatment before the
formation of a resist on a printed circuit board, or copper surface
treatment before adhesion of a flexible substrate and copper foils
in order to improve the adhesive strength between the copper foil
and a resin layer.
A multi-layer printed wiring board can be produced by piling a
plurality of the thus treated wiring boards having been formed
internal layer circuits and a plurality of prepregs obtained by
impregnating a substrate such as paper, glass cloth, etc., with a
thermosetting resin and drying, alternately, followed by pressing
with heating, by a conventional method.
This invention can be applied to the production of multi-layer
printed wiring boards obtained by adhering internal layer wiring
boards to prepregs; laminates of copper-clad laminates, wiring
boards having conductor circuits thereon and solder resists;
copper-clad laminates obtained by laminating copper foils and
prepregs; substrates for flexible wiring boards obtained by
laminating copper foils and flexible films, etc.
More concretely, the present invention can be applied to the
following embodiments.
A copper-clad laminate can be obtained by subjecting one or two
surfaces of copper foil to the surface treatment process of this
invention; laminating one or more surface treated copper foils and
one or more sheets of glass cloth or paper impregnated with an
epoxy resin, a phenol resin or a polyimide resin or one or more
sheets of an epoxy resin, a phenol resin or a polyimide resin mixed
with glass fibers, or laminating one or more the thus surface
treated copper foils coated with an epoxy resin, a phenol resin or
a polyimide resin; and subjecting to heating and pressing treatment
to form a laminated unit having copper layers on the outermost
surfaces.
A copper-clad flexible film can be obtained by subjecting one or
both surfaces of copper foil to the surface treatment process of
this invention; and bonding a flexible resin film to the resulting
copper foil using an adhesive of epoxy resin or acrylic resin so as
to have copper layers on the outermost surfaces, wherein the
flexible resin film is made from polyimide, polyester,
polytetrafluoroethylene, polysulfone, or polyether ether
ketone.
A multi-layer wiring board can be obtained by laminating one or
more copper foils and one or more sheets of glass cloth or paper
impregnated with an epoxy resin, a phenol resin or a polyimide
resin or one or more sheets of an epoxy resin, a phenol resin or a
polyimide resin mixed with glass fibers, or laminating one or more
copper foils coated with an epoxy resin, a phenol resin or a
polyimide resin; subjecting to heating and pressing treatment to
form a copper-clad laminate; removing unnecessary portions from the
copper foil of the laminate by etching to form a circuit pattern
for an internal layer; subjecting the copper foil thus treated to
the surface treatment process of this invention; laminating on the
resulting copper surface an epoxy resin, a phenol resin or a
polyimide resin, or a glass cloth or paper impregnated with an
epoxy resin, a phenol resin or a polyimide resin, or laminating a
sheet of an epoxy resin, a phenol resin or a polyimide resin mixed
with glass fibers, with repetition of laminating to form a multiple
layers and a copper foil as an outermost layer; subjecting to
heating and pressing treatment to form a laminated unit having
copper layers on the outermost surfaces; drilling through-holes in
the laminated unit; metallizing inner walls of the through-holes;
and removing unnecessary portions from the outermost copper layers
by etching to form circuits.
A multi-layer wiring board can also be obtained by laminating one
or more copper foils and one or more sheets of glass cloth or paper
impregnated with an epoxy resin, a phenol resin or a polyimide
resin or one or more sheets of an epoxy resin, a phenol resin or a
polyimide resin mixed with glass fibers, or laminating one or more
copper foils coated with an epoxy resin, a phenol resin or a
polyimide resin; subjecting to heating and pressing treatment to
form a copper-clad laminate; removing unnecessary portions from the
copper foil of the laminate by etching to form a circuit pattern
for an internal layer; subjecting the copper foil thus treated to
the surface treatment process of this invention; laminating on the
resulting copper surface an epoxy resin, a phenol resin or a
polyimide resin, or a glass cloth or paper impregnated with an
epoxy resin, a phenol resin or a polyimide resin, or laminating a
sheet of an epoxy resin, a phenol resin or a polyimide resin mixing
with glass fibers, with repetition of laminating to form a multiple
layers and a copper foil subjected to the surface treatment process
of this invention as an outermost layer; subjecting to heating and
pressing treatment to form a laminated unit having copper layers on
the outermost surfaces; drilling through-holes in the laminated
unit; metallizing inner walls of the through-holes; and removing
unnecessary portions from the outermost copper layers by etching to
form circuits.
Further, a flexible wiring board can be obtained by bonding a
copper foil to a flexible resin film using an adhesive of epoxy
resin or acrylic resin to form a copper-clad flexible film;
removing unnecessary portions from the copper foil by etching to
form a circuit pattern for an inner layer; subjecting the copper
foil thus treated to the surface treatment process of this
invention; and bonding a flexible resin film from which unnecessary
portions for connection are removed to the thus treated copper
surface with an adhesive of epoxy resin or acrylic resin, wherein
the flexible resin film is made from polyimide, polyester,
polytetrafluoroethylene, polysulfone, or polyether ether
ketone.
The resin layers can be used in the form of a prepreg, film,
curtain coat, etc. As the resin, there can be used thermosetting
resins such as phenol resins, epoxy resins, polyesters, polyimides,
etc.; thermoplastic resins such as polytetrafluoroethylene,
polysulfones, polyether sulfones, polyetherimides, etc.
This invention is illustrated by way of the following Examples, in
which all percents are by weight unless otherwise specified.
EXAMPLE 1
A copper-clad laminate for internal layer having internal layer
circuits thereon was subjected to roughening treatment with an
aqueous solution of ammonium persulfate, followed by the formation
of a copper oxide layer using the following treating solution:
______________________________________ Sodium hydroxide 0.5%
Trisodium phosphate 1.5% Sodium chlorite 3% Pure water 95%
Temperature 75.degree. C. Treating time 2 minutes
______________________________________
The thus treated laminate was dipped in the following aqueous
aldehyde solution:
______________________________________ 37% CH.sub.2 O 0.6 mole/l
Pure water making the total volume 1 liter Temperature 60.degree.
C. ______________________________________
The copper oxide layer surface was contacted with a metallic copper
plate for 3 seconds in the aqueous aldehyde solution to apply a
proper potential. The metallic copper plate had been degreased and
polished to remove rust previously. The laminate was continued to
be placed in the aqueous aldehyde solution for 120 seconds. The
potential of the treated surface was -900 mV in terms of Ag-AgCl
electrode.
Then, both sides of the resulting copper-clad laminate were
sandwiched by a pair of epoxy resin prepregs, followed by
sandwiching with a pair of copper foils and, pressed with heating
(pressure 60 kg/cm.sup.2, temperature 170.degree. C., time 120
minutes) to produce a multi-layer copper-clad laminate having
internal layer circuits therein.
The obtained multi-layer copper-clad laminate was subjected to the
following tests:
(i) Internal layer copper foil peeling test
JIS-C 6481
(ii) Resistance to hydrochloric acid
A sample of 130 mm .times. 30 mm was cut out and the surface copper
foils were removed, followed by drilling of 36 holes, each hole
having a diameter of 1 mm. Then, the sample was dipped in 19% HCl
and state of the laminate was observed after predetermined time
(minutes). The mark o means "no change". The mark x means "not
usable practically".
(iii) Resistance to electroless copper plating solution
A sample of 130 mm .times. 30 mm was cut out and the surface copper
foils were removed, followed by drilling of 36 holes, each hole
having a diameter of 1 mm. Then, the sample was dipped in the
following electroless copper plating solution and penetration of
the electroless copper plating solution into internal layers was
observed after predetermined time (hours). The mark o means "no
change". The mark x means "penetrated".
______________________________________ CuSO.sub.4.5H.sub.2 O 10 g/l
EDTA/2Na 30 g/l 37% CH.sub.2 O 5 ml/l pH 12.5 (adjusted with NaOH)
Pure water making the total volume 1 liter
______________________________________
The results are shown in Table 1.
COMPARATIVE EXAMPLE 1
The process of Example 1 was repeated except for not applying a
potential by contacting with the metallic copper plate and making
the dipping time in the aqueous aldehyde solution 60 minutes. The
potential of the copper oxide layer after 60 minutes dipping was
-130 mV in terms of Ag-AgCl electrode.
The resulting laminate was tested in the same manner as described
in Example 1. The results are shown in Table 1.
TABLE 1 ______________________________________ Example No.
Comparative Example 1 Example 1
______________________________________ Internal layer 1.2 1.1
peeling test (kgf/cm) Resistance to 20 o x HCl (min) 30 o x 40 o x
50 o x 60 o x 90 o x Resistance to 1 o x electroless 3 o x copper
plating 5 o x solution (hrs) 10 o x 15 o x 20 o x
______________________________________
EXAMPLE 2
A printed wiring board for internal layer having internal layer
circuits thereon was subjected to roughening treatment with an
aqueous solution of ammonium persulfate, followed by the formation
of a copper oxide layer using the following treating solution:
______________________________________ Sodium hydroxide 15 g/l
Trisodium phosphate 30 g/l (NaPO.sub.4.12H.sub.2 O) Sodium chlorite
90 g/l Pure water making the total volume 1 liter Temperature
85.degree. C. Treating time 120 seconds
______________________________________
The resulting internal layer wiring board having a copper oxide
layer thereon was washed with water.
A roll for transporting the internal layer wiring board was
installed in an aqueous solution of 37% formaldehyde with pH of
12.5 and concentration of 5 ml/l to reduce the copper oxide. The
roll was obtained by coating a copper plated cloth (manufactured by
Seren K.K.), the surface of which had been plated with gold, on a
rubber-made roll. The temperature of the aqueous aldehyde solution
for reducing copper oxide was made 50.degree. C. The internal layer
wiring board was passed through the roll at a rate of 40 cm/min and
contacted with the aqueous aldehyde solution for 5 minutes. After
washing with water, the thus treated wiring board was dried at
80.degree. C. for 30 minutes. Both sides of the wiring board was
sandwiched with a pair of epoxy resin prepreg, followed by
sandwiching with a pair of copper foils and, pressed with heating
(pressure 60 kg/cm.sup.2, temperature 170.degree. C, time 120
minutes) to prepare a multi-layer copper-clad laminate having
internal layer circuits therein.
The obtained multi-layer copper-clad laminate was subjected to the
same test as in Example 1. The results are shown in Table 2.
COMPARATIVE EXAMPLE 2
The process of Example 2 was repeated except for not reducing the
copper oxide layer in the aqueous aldehyde solution nor contacted
with the metal coated roller.
The obtained multi-layer copper-clad laminate was subjected to the
same test as in Example 1. The results are shown in Table 2.
TABLE 2 ______________________________________ Example No.
Comparative Example 2 Example 2
______________________________________ Internal layer 1.2 1.1
peeling test (kgf/cm) Resistance to 20 o x HCl (min) 30 o x 40 o x
50 o x 60 o x 90 o x Resistance to 1 o x electroless 3 o x copper
plating 5 o x solution (hrs) 10 o x 15 o x 20 o x
______________________________________
EXAMPLE 3
A printed wiring board for internal layer having internal layer
circuits thereon was subjected to roughening treatment with an
aqueous solution of ammonium persulfate, followed by the formation
of a copper oxide layer using the following treatment solution:
______________________________________ Sodium hydroxide 15 g/l
Trisodium phosphate 30 g/l (Na.sub.3 PO.sub.4.12H.sub.2 O) Sodium
chlorite 90 g/l Pure water making the total volume 1 liter
Temperature 85.degree. C. Treating time 90 seconds
______________________________________
The resulting internal layer wiring board having a copper oxide
layer thereon was washed with water, followed by the treatment with
the following treating solution:
______________________________________ Sodium borohydride 1 g/l
Pure water making the total volume 1 liter pH 12.5 Temperature
40.degree. C. Treating time 40 seconds Potential of copper -800 mV
surface ______________________________________
The thus treated wiring board was treated with the following
aldehyde solution:
______________________________________ 36% CH.sub.2 O 4 ml/l Pure
water making the total volume 1 liter pH 12.5 Temperature
50.degree. C. Treating time 5 minutes
______________________________________
The thus treated wiring board was washed with water and dried at
80.degree. C. for 30 minutes. Both sides of the wiring board was
sandwiched with a pair of epoxymodified polyimide resin prepregs
(I-67, a trade name, mfd. by Hitachi Chemical Co., Ltd.), followed
by sandwiching with a pair of copper foils of 35 .mu.m thick and
pressed with heating (pressure 50 kg/cm.sup.2, temperature
170.degree. C., time 90 minutes) to prepare a sample laminate.
COMPARATIVE EXAMPLE 3
The process of Example 3 was repeated except for not subjected to
the treatment with the aqueous formaldehyde solution and changing
the treating time with the aqueous solution of sodium borohydride
to 10 minutes in place of 40 seconds.
COMPARATIVE EXAMPLE 4
The process of Example 3 was repeated except for not subjected to
the treatment with the aqueous solution of sodium borohydride.
The sample laminates obtained in Example 3 and Comparative Examples
3 and 4 were tested in the same manner as described in Example 1.
The results are shown in Table 3.
TABLE 3 ______________________________________ Comparative
Comparative Example No. Example 3 Example 3 Example 4
______________________________________ Internal layer 0.90 0.60 1.0
peeling test (kg/cm) Surface Uniform Uneven Uniform appearance
Resistance to No change No change Penetrated in HCl the whole
(20-90 mins.) cases Resistance to No change No change No change
electroless until 5 hrs. copper plating Over 10 hrs., solution
penetrated (1-20 hrs.) considerably.
______________________________________
As explained above, according to this invention, adhesion between a
resin material such as a prepreg and copper of a conductor circuit,
and the like can be improved. Further, the resulting multi-layer
printed wiring boards are excellent in resistance to hydrochloric
acid and resistance to an electroless copper plating solution.
* * * * *